A glycated protein is generated non-enzymatically via a covalent bond between an amino group on a protein and the reducing terminal of a sugar, and is also referred to as an Amadori compound. In blood, glucose is bound to valine at the N-terminal of the β-chain of hemoglobin to generate glycated hemoglobin (glycohemoglobin; HbA1c). The abundance ratio of HbA1c to hemoglobin (Hb) is higher in patients suffering from diabetes mellitus as compared with a normal healthy individual, and the concentration of HbA1c in blood is known to reflect the blood-sugar level during the past several weeks. Thus, concentration of HbA1c in blood is quite important in clinical tests for diagnosis of diabetes mellitus and in blood-sugar control of patients suffering from diabetes mellitus. The HbA1c concentration in blood may be measured using an enzyme having specificity to fructosyl valine.
Fructosyl amino acid oxidase is an FAD-dependent enzyme which catalyzes a reaction where fructosyl amino acid is oxidized to generate 2-keto-D-glucose and the corresponding amino acid. Fructosyl amino acid oxidases have been isolated from various kinds of organisms and it has been suggested that glycated protein such as glycated albumin, HbA1c and fructosamine may be analyzed using such enzymes.
In order to assay HbA1c with a high specificity, the fructosyl amino acid oxidase preferably has a selectivity toward fructosyl valine compared to fructosyl lysine. More preferably, the fructosyl amino acid oxidase may have an oxidase activity toward fructosyl valyl histidine, which corresponds to the N-terminal two amino acid resides of Hb. Hirokawa et al. (Biochem Biophys Res Commun, 311(1), 2003, 104-111) discloses fructosyl peptidyl oxidases derived from filamentous bacteria of the genus Achaetomiella and Chaetomius. 
One non-limiting object of the present application is to provide a new fructosyl peptidyl oxidase for use in measurement of glycated proteins. Further objects, embodiments, forms, features, advantages, aspects, and benefits shall become apparent from the following description and drawings.